Different colors, lengths, and of lane markings guide users of roads, e.g., drivers and pedestrians. When a vehicle is equipped with a camera and processor, the markings can be analyzed using computer vision techniques, U.S. patents and Publications: U.S. Pat. Nos. 7,421,095, 7,421,095, 7,140,803, 2008-0255724, 2007-0225913, and 2007-0198146, 2006-0177265, and 2006-0132295.